A fuel cell system such as a household cogeneration system has a fuel treatment device that produces fuel gas containing hydrogen and a fuel cell that generates power using the fuel gas produced by the fuel treatment device.
The fuel treatment device has a reforming section that produces hydrogen-rich gas containing hydrogen as a main component by steam-reforming reaction from steam and raw material gas such as hydrocarbon fuel, and a carbon monoxide removing section that removes carbon monoxide from the hydrogen-rich gas since carbon monoxide has an action of poisoning a catalyst of a fuel cell.
The carbon monoxide removing section also has: a converting section that decreases carbon monoxide concentration in the hydrogen-rich gas to about 0.5% by shift reaction of a CO converting catalysis; a selective oxidizing section that decreases the carbon monoxide concentration in the hydrogen-rich gas to about 10 ppm or less by selective oxidation reaction of a CO selective oxidation catalysis; and a mixing channel that connects the converting section and the selective oxidizing section. The mixing channel is a passage for mixing the hydrogen-rich gas exhausted from the converting section with air. For mixture of the hydrogen-rich gas and air in the mixing channel, a method of supplying air to the mixing channel in which the hydrogen-rich gas flows is known (refer to, for example, Patent Document 1).
FIGS. 1A and 1B are cross sectional views of a mixing channel in a fuel treatment device already proposed (refer to, for example, Patent Document 1).
As shown in FIGS. 1A and 1B, mixing channel 10 connects converting section 20 and selective oxidizing section 30. Mixing channel 10 is also connected to an air supply pipe (40, 41). The air supply pipe (40, 41) extends to the center of a transverse section of mixing channel 10. Broken-line arrows in FIGS. 1A and 1B show the flow of the hydrogen-rich gas, and solid-line arrows show the flow of air.
As shown in FIG. 1A, by supplying air into mixing channel 10 in which hydrogen-rich gas flows via the air supply pipe 40, the hydrogen-rich gas and air can be mixed. As shown in FIG. 1B, by supplying air into mixing channel 10 in which the hydrogen-rich gas flows via a plurality of openings 42 formed at an end of air supply pipe 41, the hydrogen-rich gas and the air can be mixed.
Since the air supply pipe extends to the center of the transverse section of mixing channel 10, air is supplied to the center of the transverse section of mixing channel 10 at which flow velocity of the hydrogen-rich gas is fast, and mixing of the hydrogen-rich gas with air can be promoted.
Normally, the flow rate of the hydrogen-rich gas flowing in mixing channel 10 is about 20 times as high as that of air supplied from the air supply pipe.
As described above, when the flow rate of the hydrogen-rich gas flowing in the mixing channel is high and the flow rate of air supplied is low, the flow velocity of air is low, and an eddy formed in the mixing channel by supply of air is small. When an eddy formed is small, the hydrogen-rich gas and air are not sufficiently mixed in the mixing channel. Although it is also considered to make an air ejection hole small in order to increase the flow velocity of air, in this case, pressure loss increases.
Since the flow rate of the hydrogen-rich gas is high as described above, the method of supplying air in the mixing channel in which the hydrogen-rich gas flows as shown in FIGS. 1A and 1B also has a problem that the pressure loss becomes large.
As described above, the method of supplying air into the mixing channel in which the hydrogen-rich gas flows as shown in FIGS. 1A and 1B has problems that mixing of the hydrogen-rich gas with air is insufficient and that the pressure loss is large.
To solve such problems, a method of supplying the hydrogen-rich gas into the mixing channel in which air flows has been proposed (refer to, for example, Patent Document 2). FIG. 2 is a perspective view of mixing channel 10 in a fuel treatment device disclosed in Patent Document 2.
As shown in FIG. 2, mixing channel 10 passes through room 50 filled with the hydrogen-rich gas and has a plurality of gas supply ports 11. The gas supply ports are formed over the entire length of mixing channel 10. The upstream end of mixing channel 10 is connected to the air supply section, and the downstream end of mixing channel 10 is connected to the selective oxidizing section.
A step of mixing the hydrogen-rich gas with air in mixing channel 10 shown in FIG. 2 will now be described. First, air is supplied from the air supplying section into mixing channel 10. Then, the hydrogen-rich gas is supplied into mixing channel 10 via gas supply ports 11 provided in the mixing channel.
In the method to supply the hydrogen-rich gas into the mixing channel in which air flows as shown in FIG. 2, the hydrogen-rich gas having high flow rate is supplied into the mixing channel in which air having low flow rate flows, so that the hydrogen-rich gas is supplied into the mixing channel at high flow velocity. Consequently, as compared with the mixing channel shown in FIGS. 1A and 1B, the hydrogen-rich gas and air can be mixed more efficiently.